New Paper on Einstein@Home Radio Pulsar Discovery

Benjamin Knispel
Benjamin Knispel
Joined: 1 Jun 06
Posts: 129
Credit: 4,974,142
RAC: 0
Topic 198055

Hi all,

today you can find the latest Einstein@Home paper here on the arXiv preprint server. If you want to read it, just click on the PDF button on the upper right on the arXiv page.

What is this new paper about?
Our paper presents the discovery of a millisecond pulsar found in Pulsar ALFA survey observations with the Arecibo telescope, processed on Einstein@Home as part of the BRP4 search. The pulsar rotates once every 4.3 milliseconds and is in 22-day orbit with a companion star of ~0.3 solar masses. This makes it look like a so-called “recycled†pulsar that was spun up to this rapid rotation in the past by [url=http://en.wikipedia.org/wiki/Accretion_(astrophysics)]accretion of matter[/url] from its companion. This recycling process usually leads to almost perfectly circular orbits in the binary systems. For PSR J1950+2414 (that's its name) however, this did not happen!

What is special about this radio pulsar?
The odd – and interesting – thing about PSR J1950+2414 is that the orbit is not circular, but elliptic with an orbital eccentricity of e=0.08 (e=0 would be a circle; e=0.08 is just short of the famously elliptical orbit of Mars around the Sun). That is far above that what is known from other recycled pulsars (usually e < 0.001 and much smaller) and it is not compatible with the standard “recycling scenarioâ€. This pulsar system must have formed in some other way! There are several possibilities how this system might have evolved. We currently cannot say for certain through which of these possible channels the system formed.

Interestingly, there are three other very similar systems (in terms of their orbits and spins). So one might speculate that there is a common mechanism that generates this kind of pulsar system; again we do not know for certain which mechanism that could be. Also, it could of course be simply a coincidence that these system look similar.

How does the Universe make pulsars like this one?
In our paper we look at four different mechanisms and how well they can explain PSR J1950+2414's characteristics and those of the other three known similar pulsars:

a) initial evolution of the pulsar in a triple system which became dynamically unstable.
Here you have initially a triple system with a pulsar (yes, this does exist and is really awesome!), which over time ejects one of its members. The four known systems could of course have formed this way, however their similarity would have to be a (unlikely) coincidence. Three-body systems are chaotic and the resulting binaries should be very different from one another.

b) origin in an exchange encounter in an environment with high stellar density, like that of the core of a globular cluster.
In this case the pulsar is born via the standard scenario and in an almost circular orbit. It is inside a region of space with lots of other stars (like a globular cluster). There are lots of millisecond pulsars in globular clusters, so this is something well known. At some point the binary system has a close encounter with a third star. A new binary system with an elliptical orbit forms and it gets ejected from the globular cluster. The problem here is that there is no globular cluster near the pulsar, and that the pulsar is very close to the disk of our Galaxy – unlike your average globular cluster. Again: possible, but unlikely.

c) rotationally delayed accretion-induced collapse of a super-Chandrasekhar white dwarf.
Here, your neutron star/pulsar does not form in a supernova and gets spun up afterwards via accretion from its companion star over hundreds of thousands or billions of years. (This long time and the tidal forces during this period are what circularizes the orbits of “normal†millisecond pulsars.) Here, after the accretion phase the system consists of two white dwarf stars in a circular orbit. One of them is actually too massive to exist as a (non-rotating) white dwarf (that's the “super-Chandrasekhar†in the name, it's above the Chandrasekhar mass limit of ~1.4 solar masses). Luckily, it's spinning rapidly enough to avoid collapsing to a neutron star under its own gravity – at least for some time. When it has spun down (various ways of losing angular momentum are possible here), at some point it has to collapse to neutron star. This releases a lot of gravitational binding energy and ejects some matter into a disk around the system and it also makes the orbit eccentric. Making reasonable assumptions, these leads to the values observed for the four similar pulsars. You can read more about this in this paper.

d) dynamical interaction of the binary with a circumbinary disk.
Here again the rapidly rotating pulsar forms through the usual channel, and the orbital eccentricity arises from the gravitational interaction with a circumbinary disk ejected from the stars at earlier times. This is a possibility that would explain the similar systems. Again, here is the paper describing this mechanism in more detail

So none of the models is out of the race, although a) and b) seem unlikely. Both c) and d) make rather precise predictions for the masses of the pulsar and the companion star. Unfortunately, we cannot determine either precisely enough at the moment. But further observations with the Arecibo telescope are ongoing and should let us make those assessments in the future. At this point we might be able to say whether c) or d) or neither is a good candidate to explain systems like J1950+2414.

Thank you!
Big thanks to all of you for supporting Einstein@Home and making this possible! If you have any questions, just let me know. I know that there are a lot of technical terms in what I wrote up here, and I tried to link to additional info. If you have questions, I'd be happy to answer them here. :-)

Cheers, Benjamin

P.S.: I have also submitted the paper to The Astrophysical Journal for publication. It will now go the usual path of all scientific publications. It has passed first quality control and internal review and will now be sent to two independent scientists for peer-review. Theses referees will send back reports about our paper to the journal. The reports can be anything from “please accept for publication as is†to “should not be published in this journalâ€, but in most cases they will ask for clarifications, re-writes of sections, or offer insights that can help to improve the science in the paper. The paper will be re-submitted by us after we have addressed the comments and it goes to the referees for another round of comments until they are happy with it and recommend it for publication. We'll keep you posted about the progress of that.

P.P.S.: If your computer finds a pulsar, you will not only get our lovely certificates, you will also get mentioned in the paper. If you look at the acknowledgements section of this paper, you will find: “We thank all Einstein@Home volunteers, especially those whose computers found PSR J1950+2414 with the highest statistical significance: David Miller, Cheltenham, Gloucestershire, UK and `georges01'.â€

 

Einstein@Home Project

astro-marwil
astro-marwil
Joined: 28 May 05
Posts: 420
Credit: 148,742,774
RAC: 4,814

New Paper on Einstein@Home Radio Pulsar Discovery

Hallo Benjamin!
Congratulations for this discovery. We cross our fingers for a short, successful evaluation process.

On page 3 there is more than half of a page for describing the purpose, results and achievments of E@H.

It´s somewhat astonishing to me, that this relative strong signal wasn´t found before.
If I convert the published significance of S = 120,8 to statistical error, I get an accuracy of estimated 10sigma or so. Is it right?

Kind regards and happy crunching
Martin

astro-marwil
astro-marwil
Joined: 28 May 05
Posts: 420
Credit: 148,742,774
RAC: 4,814

Hallo Benjamin! Why not

Hallo Benjamin!
Why not putting a hint for this on the homepage/news and in BOINC manager on the information page?
These papers are important arguments to our detractors and for us something like the fuel driving the motor.

Kind regards and happy crunching
Martin

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,020
Credit: 102,364,770
RAC: 126,174

Martin : I think we ought

Martin : I think we ought focus on thanking our contributors and not be concerned with addressing the 101st Chairborne at all. They will be randomly right one day out of pure chance at least, so let Lady Luck sort them out. We are here for our volunteer contributors who did actually assist in this result, and not for those who might have but for attempts to redefine this project's aims & processes in the service of their private psychological needs. Such immature attention seeking behaviour may be managed as per mischievous squeaky wheels : let them pass on by un-oiled. :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Benjamin Knispel
Benjamin Knispel
Joined: 1 Jun 06
Posts: 129
Credit: 4,974,142
RAC: 0

Hi

Hi Martin,

Quote:
(…)We cross our fingers for a short, successful evaluation process.

Thank you!

Quote:
It´s somewhat astonishing to me, that this relative strong signal wasn´t found before.

If you are wondering why earlier surveys did not find this: the signal is strongly dispersed and the pulsar is spinning rapidly. To detect such a signal you need narrow radio channels (a fine frequency resolution) in your observing instrument and backend. This is one of the things that earlier surveys were not so good at.

The pulsar was discovered quite a while ago and had been published soon after that on our BRP4 discovery page and was also probably announced in the forums or as a news item. The paper also states the discovery date as 2011 Oct 4. It was found in data from April 4. The fact that we found it and not some other PALFA collaboration pipeline probably is just due to the fact that Einstein@Home was the first to look at this particular data set. It also just as often that it is the other way around.

Why did it take so long for the publication, anyway? The thing with pulsars is that you have to observe them for at least one year to measure their various parameters to a high precision. Otherwise there is no way to know exactly where they are in the sky, what their spin-down is (i.e., how fast they lose energy from their rotation), nor is it possible to measure the relativistic effects in their orbits.

For example in this case, we can measure the relativistic periastron advance of the pulsar orbit and find it to be 0.0020 ± 0.0003 degrees per year, or roughly 1/500th of a degree per year. This is really, really small and it's absolutely mind-boggling that we can still measure this to this level of precision. But it's only possible if you observe for long enough.

Quote:
If I convert the published significance of S = 120,8 to statistical error, I get an accuracy of estimated 10sigma or so. Is it right?

S=120.8 means a false alarm probability of 10^-120.8; so that should be way more than 10 sigma! I'd have to look this up somewhere to tell you how much that is in sigma, but I'd always prefer the false-alarm probability (or significance), because it automatically tells you how likely it is that this is real or not. And a chance of 10^-120.8 that it is just random noise fluctuations is very, very, very small :-)

Cheers,
Benjamin

 

Einstein@Home Project

Benjamin Knispel
Benjamin Knispel
Joined: 1 Jun 06
Posts: 129
Credit: 4,974,142
RAC: 0

Hi again, RE: Why

Hi again,

Quote:
Why not putting a hint for this on the homepage/news and in BOINC manager on the information page? These papers are important arguments to our detractors and for us something like the fuel driving the motor.

the post here is just to keep you guys here up to date with what's going on “in the backgroundâ€. The paper has just been submitted, and while we are confident that we did a good job in writing up our results, there is still some way to go until it is officially published and “doneâ€.

Once it is officially published we will certainly have a news item here on our webpages and via the BOINC Manager. But for now we will just stick to this thread and to answering any questions that might pop up. And as Mike said we should not be too concerned with the “addressing the 101st Chairborne†– had to look up the meaning of that phrase, though :-)

Cheers,
Benjamin

 

Einstein@Home Project

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,020
Credit: 102,364,770
RAC: 126,174

The 'super-Chandrasekhar'

The 'super-Chandrasekhar' aspect I find fascinating. It is 'super' as in more massive than traditional calculations. But it is also 'super' as in 'supersaturated' ie. held out of a phase change much like dew points etc with air/water mixtures, but thinking here of the equation of state of a white dwarf vs that of a neutron star. So that would be a busy time of much change for these systems when the 'condensation' finally happens.

So in generality can one think of the whole line/sequence of scenarios from fusing stars -> white dwarfs -> neutron stars -> black holes as state changes progressing due to loss of energy via various radiations ??

[ Gravity and entropy are patient adversaries that always win in the end .... ]

Cheers, Mike.

( edit ) That is : white dwarfs relying on electron state degeneracy progressing to neutron stars relying on neutron state degeneracy, fermions both thus Pauli exclusion applies. Makes one wonder if there is a supreme matter state similiarly relying on degeneracy ( of what ?! ) that would prevent black holes having the singularity. I vote for that .... :-)

( edit ) ASIDE : I have recently watched the movie "Interstellar" and thus my mind is full of gravitational what-iffery. A very good production I will add and has several gorgeous scenes of CGI 'numerical relativity' done with the assistance of Kip Thorne.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Benjamin Knispel
Benjamin Knispel
Joined: 1 Jun 06
Posts: 129
Credit: 4,974,142
RAC: 0

Hi all, just a quick

Hi all,

just a quick update on the progress of the paper: We have receive a very nice and useful referee report only six days after submitting the paper to the journal.

The report is useful in two ways: 1) It is very positive and basically recommends the paper for publication after small adjustments. 2) It contains good advice on how to improve the paper by clarifying certain parts of the manuscript, adding missing references, or re-phrasing some sentences.

After not having a lot of time over the week, I spent some time this morning to address most of the comments, and hope to be ready early next week to re-submit the paper for another round of review.

Cheers,
Benjamin

 

Einstein@Home Project

Trotador
Trotador
Joined: 2 May 13
Posts: 57
Credit: 901,259,884
RAC: 1,044,085

RE: Hi all, just a quick

Quote:

Hi all,

just a quick update on the progress of the paper: We have receive a very nice and useful referee report only six days after submitting the paper to the journal.

The report is useful in two ways: 1) It is very positive and basically recommends the paper for publication after small adjustments. 2) It contains good advice on how to improve the paper by clarifying certain parts of the manuscript, adding missing references, or re-phrasing some sentences.

After not having a lot of time over the week, I spent some time this morning to address most of the comments, and hope to be ready early next week to re-submit the paper for another round of review.

Cheers,
Benjamin

Good job, congratulations!

Bikeman (Heinz-Bernd Eggenstein)
Bikeman (Heinz-...
Moderator
Joined: 28 Aug 06
Posts: 3,515
Credit: 427,081,672
RAC: 188,692

BTW in the meantime Benjamin

BTW in the meantime Benjamin updated the paper to version 2 here:

http://arxiv.org/abs/1504.03684v2

and it has now been accepted for publication in The Astrophysical Journal.

Congrats!

HB

Bikeman (Heinz-Bernd Eggenstein)
Bikeman (Heinz-...
Moderator
Joined: 28 Aug 06
Posts: 3,515
Credit: 427,081,672
RAC: 188,692

BTW, for those who find the

BTW, for those who find the original paper on the proposed new way thru which some of the very fast spinning neutron stars might be created too technical, there was a Sky and Telescope article on it some time ago. This article doesn't mention Einstein@Home because it was written well before the E@H discovery discussed here. It stated that

Quote:
The key will now be to find more systems like these two and see whether they match all the scenario’s tight constraints.

which is what the E@H discovery did.

Cheers
HB

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.